1. Field of the Invention
The present invention relates to a zoom lens barrel having a device for detecting a variation in focal length during zooming. In particular, the present invention relates to an apparatus for determining a variation in focal length which includes a zoom code plate and a zoom brush contacted therewith.
2. Description of Related Art
In conventional zoom lens barrels, such as those used in still cameras for example, devices equipped with a zoom code plate and a zoom brush, supported respectively by an outer ring and by an inner ring which move relatively during zooming, are often used as a means for detecting a focal length during zooming. In such a device, when the outer ring and the inner ring move relatively during zooming, the zoom brush is slid while contacting a conductive pattern formed on the zoom code plate, and a signal corresponding to a current focal length is outputted to a camera operation control circuit. Based on this signal, the camera operation control circuit inputs data, from a data table which may be prepared for any variable information, corresponding to the focal length at that time.
In the prior art, zoom lens barrels having such a focal length detecting device have been assembled in a manner such that the zoom brush is fixed to the zoom brush supporting part on the inner ring by screws, adhesives or the like. This results in a time consuming assembly operation, poor production efficiency, and additionally once the zoom brush has been fixed, it is very difficult to detach it.